A storage type water heater includes a tank to contain water to be heated. Cold water is introduced into the lower end of the tank while heated water is withdrawn from an outlet in the upper head of the tank. The water heater tank is normally composed of steel, and to prevent corrosion of the steel tank, a corrosion resistant coating, formed of vitreous enamel or plastic is normally applied to the inner surface of the tank. In practice it is difficult to completely coat certain areas of the steel tank, such as areas bordering openings in the tank or the joints between the cylindrical shell and heads of the tank. In addition, the corrosion resistant coating may contain minor imperfections. As a result, intensified corrosion can occur at the exposed steel areas of the tank.
As a consequence, it has been the practice to mount an anode formed of a metal electro-negative to steel, such as aluminum, zinc or magnesium, in the tank. The anode generally takes the form of an elongated rod and the upper end of the anode extends through an opening in the upper head of the tank and is supported from an annular spud that is welded to the outer surface of the upper head. With the use of an anode, a galvanic circuit is set up in which the anode will corrode preferentially to thereby prevent corrosion of the exposed areas of the steel tank.
However, the use of an anode normally requires a separate opening in the tank head. Therefore, it has been proposed to combine an anode mount and a hot water outlet so that only a single opening in the upper head is required. U.S. Pat. No. 4,060,472 describes a combination anode mount and hot water outlet which includes a plastic tube that extends downwardly through an opening in the upper head of the tank and the plastic tube is provided with a transverse wall that divides the tube into an upper water outlet chamber and a lower chamber. Openings are provided in the wall of the plastic tube and establish communication between the tank and the upper chamber of the tube, thereby serving to conduct heated water from the tank through the tube to the water piping system.
In the construction of the aforementioned patent, the upper end of an anode rod is mounted in the lower chamber of the plastic tube and a metal sleeve is molded in the plastic tube and provides an electrical connection between the upper end of the anode and a metal nipple which is located on the outer surface of the upper end of the plastic tube. The nipple is threaded in a stud welded to the upper head of the tank and bordering the opening in the tank.
With the construction of U.S. Pat. No. 4,060,472 the plastic tube, metal sleeve and anode are locked together by compression rolling.
It has been found that with the construction of the aforementioned patent, leakage can occur between the nipple and the plastic tube, thereby causing corrosion of the upper end of the internal metal sleeve. Similarly, leakage can also occur between the anode and the plastic tube resulting in corrosion of the lower end of the metal sleeve. Corrosion of the metal sleeve will increase the electrical resistance and thus reduce the effectiveness of the anode. In certain situations, the corrosion may be so severe that the electrical connection between the anode and the nipple is destroyed.